CEMEX UK Cement Ltd Southam Quarry ROMP Environmental Statement

7 Geology and Hydrogeology

7.1 Introduction This section considers the geology and hydrogeology of Southam Quarry and the potential impacts of the operation and restoration of the site.

7.1.1 Methodology In order to assess the likely impacts on geology and hydrogeology associated with the operation and restoration, and to compare these with pre-existing conditions, it is necessary to define the baseline conditions. This involves characterising the existing geology and hydrogeology, with particular reference to the permeability of underlying soils and bedrock, aquifer exploitation potential and groundwater quality. The baseline conditions for this assessment are taken from an operational quarry. These conditions provide the baseline for impact assessment to be used along with consideration of the performance of the site’s ongoing environmental controls. The findings of the assessment inform the requirement for, and extent of, mitigation measures to provide for protection of local water resources and the geological resource.

7.1.2 Existing data sources Information for this section has been taken from Arup’s 2010 Environmental Statement for Landfill Cell 3[2], WYG 2010 Environmental Statement for the Southam Quarry extension[3], and ESI’s (2006) Hydrogeological Risk Assessment (HRA)[4] of activities at Southam Quarry. Other key reference documents include geological and hydrogeological references including the British Geological Survey Sheet 184).

7.1.3 Groundwater Risk Assessment Conventional risk assessment methodology is used to consider potential sources of contamination, receptors that have potential to be affected and potential pathways between source and receptor. Without the three essential components of a source (hazard), pathway and receptor, there can be no risk. Thus, the presence of a hazard at a site does not mean that there will necessarily be attendant risks. An effective way of mitigating risk is to remove or minimise the pathway from source to receptor, if it is impossible to remove or reduce the contaminant source. The risk of surface water and groundwater contamination from the quarry is evaluated by considering the three components in sequence; the conceptual model is illustrated as follows:

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CEMEX UK Cement Ltd Southam Quarry ROMP Environmental Statement

7.2 Baseline Conditions

7.2.1 Geology The regional geology of the Southam Quarry area comprises approximately 40m of Jurassic Lias deposits underlain by approximately 50m of Triassic deposits including Penarth Group and Mercia Mudstone Group deposits. The strata dip 2° to the southeast. A summary of this stratigraphy is presented in Table 2. Table 2 Regional geological stratigraphic succession Period Group Formation Member Lithology Hydrogeological characteristics Jurassic Lias Blue Lias Rugby Alternating grey Secondary 20m Limestone argillaceous (minor) Aquifer Member limestone and regionally with dark grey variable mudstone. permeability. Unproductive Saltford Dark grey locally 10m Shale calcareous Member mudstone with a few thin limestone beds. Triassic Penarth Lilstock Langport Hard, Unproductive 2m Group Formation Member porcellaneous, stratum massive, regionally but micritic behaves as limestone. Pale secondary grey weathering (minor) aquifer to white or locally cream. At outcrop generally worn or pitted Cotham Grey-green and Aquitard 23m Member brown calcareous mudstone Westbury Interbedded Aquitard 2m Formation dark grey to black fissile mudstone with massive mudstone. Mercia Blue Green siltstone Aquitard 3m Mudstone Anchor and mudstone. Group Formation

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CEMEX UK Cement Ltd Southam Quarry ROMP Environmental Statement

The Jurassic Blue Lias Formation is split into two members. The top 20m comprises the Rugby Limestone Member, which consists of alternating limestones and mudstones. This is underlain by approximately 10m of Saltford Shale, which also comprises a sequence of mudstone with thin limestone beds. The limestone beds are up to 0.5m thick and make up approximately 30% of the Blue Lias formation. The upper layer of the Triassic Penarth Group, is the Lilstock Formation. This includes the Langport Member (formerly the White Lias) and the Cotham Member. The Langport Member is a thin (approximately 2m) limestone bed. This is then underlain by 23m of grey-green and brown mudstones, which make up the Cotham Member. The lower layer formation of the Penarth Group is the Westbury Formation, which is 2m thick and comprises dark grey to black fissile and massive mudstones. The Blue Anchor Formation of the Triassic Mercia Mudstone Group underlies the Penarth Group. This formation is 3m thick and is composed of green siltstone and mudstone. A summary of the stratigraphy and depths at Southam Quarry is presented in Table 3. Table 3 Stratigraphic succession at Southam Lithology Depth and elevation to base of Range of all boreholes strata Ground elevation 90.76 – 110.80 m AOD Topsoil / overburden Thickness 0 – 2.20 m Rugby Limestone Thickness up to 30.55 m Member (formerly the Elevation 77.02 – 109.74 m AOD Blue Lias) Saltford Shale Member Thickness 10.82 – 13.7m (formerly the Lower Elevation 64.7 – 88.73 m AOD Lias) Langport Member Thickness 1.63 – 2.24 m (White Lias) Elevation 62.75 – 77.91m AOD Cotham Member / Blue Thickness > 18.31m Anchor Formation

Some of the thicker limestones are persistent across the entire Southam quarry area and provide distinct marker horizons. One of these (the c 0.45m thick Calcirhynchia Bed), has been used as a boundary between two of the operational units (see below). This strong, homogenous unit has been recorded in all boreholes during the drilling, except those in the existing Spiers Farm quarry area where it has outcropped. The top of the Calcirhynchia Bed is generally c 7.5-8.0m above the base of the Blue Lias. The quarry displays the classic sequence of alternating limestones and shales of the Jurassic and Triassic periods and as such has been designated as a Local Geological Site ‘Southam Cement Quarries’ (formerly known as RIGS – Regionally Important Geological Site). The quarry therefore attracts visitors from educational establishments and geological organisations.

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CEMEX UK Cement Ltd Southam Quarry ROMP Environmental Statement

7.2.2 Operational Units The existing quarry excavations are organised in a number of ‘lifts’ or operational units, which are defined on the basis of geology (and therefore material chemistry). The established operational divisions, which are also used in this assessment are as follows: Table 4 Operational Units Operational Unit Description A Blue Lias from rockhead to top of Calcirhynchia Bed B Blue Lias from top of Calcirhynchia Bed and upper c 4m of the Lower Lias (operational base of Blue Lias) C Remaining Lower Lias from operational base of Blue Lias to top of White Lias

The underlying White Lias limestone beneath Unit C is referred to as ‘Unit D’. This has not previously been worked for use in the cement works and will not be worked in the future, partly to ensure the protection of the White Lias aquifer which is linked to ‘Holy Well’ at Southam. The chemical composition of the respective units is critical in securing the required quality and blend of material for use in the Rugby Cement Works. The mineral volumes to be extracted have been based upon the objective of maintaining a constant blend of 25% calcium oxide (CaO), and < 2.5% sulphur trioxide (SO3).

7.2.3 Hydrogeology

7.2.3.1 Groundwater Units Groundwater at Southam Quarry is located in two geological layers, the Rugby Limestone Member and the Langport Member. The EA classify the Rugby Limestone Member as a Secondary (Minor) Aquifer, whereas the Langport Member is classed as unproductive stratum (Non-Aquifer). Southam Quarry does not lie within an EA Source Protection Zone, however it was designated as a Nitrate Vulnerable Zone by DEFRA in 1996. The Groundwater Vulnerability Map (Sheet 30, Northern Cotswolds) shows the site as being underlain by a secondary aquifer, presumably referring to the Rugby Limestone Member. The Rugby Limestone Member at Southam consists of thin but laterally persistent limestones with intervening mudstones, which form a multi-layered secondary aquifer (Jones et al., 2000). At the site the aquifer is considered to be of intermediate vulnerability. Secondary aquifers are formations that can be fractured or potentially fractured rocks, which do not have high permeability, or other formations of variable permeability including unconsolidated deposits. Although not producing large quantities of water for abstraction, they are important for local supplies and in supplying baseflow to rivers. Jones et al., (2000) state that a few small springs ooze from the outcrop of the formation and at the top of the underlying less permeable Penarth Group; however, yields are low and decrease in summer. The soils overlying the Rugby Limestone Member in the area are classed as soils of intermediate leaching

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CEMEX UK Cement Ltd Southam Quarry ROMP Environmental Statement

potential which can possibly transmit a wide range of pollutants. Soils within the boundary to the north of the A426 are now absent due to quarrying.

7.2.3.2 Groundwater levels Groundwater levels within the Blue Lias have been recorded as 91 to 94m AOD between 1989 and 2000, and 83 to 93m AOD between 2004 and 2006. Groundwater levels recorded within the Langport Member over the same periods were 73 to 76mAOD and 73 to 77mAOD respectively. No regional groundwater level data are available within 5km of the site. Between November 1988 and 1991 the quarry lake water level varied by at least 2-3 m but was generally in the range of 75 to 77 m AOD (Geoffrey Walton Associates, 1991). Lake levels rose in the winter and spring and were reported to fall in the summer probably by seepage through thin cover into the underlying Langport Member (White Lias). Water is currently pumped from the Spiers Farm quarry void to the old quarry lake (areas I and II), with the lake water level being maintained at between 75.49- 78m AOD.

7.2.3.3 Groundwater regime MORECS data from 1971 to 2000 has been analysed to establish the amount of hydrologically effective rainfall (HER) in the area. For MORECS square 137, which contains Southam Quarry, the HER was calculated as 158mm per year. Vertical groundwater flow is likely to take place slowly though the clay layers of the Blue Lias and Lower Lias towards the Langport Member. Lateral flow may occur within the limestone beds, which are common within the Rugby Limestone Member but rare within the Saltford Shale Member. This flow occurs though the fractures within the limestone at a wide range of velocities. The main areas of recharge within the Langport Member are reported to be from rainwater falling on the Langport Member outcrops to the west and north, and from water running into the quarry area where the Langport Member is exposed. Groundwater discharge is considered to be to the south and west to surface water. This would suggest a local groundwater flow under the site to the south and west. It is believed that flows through the Langport Member supply the Holy Well.

7.2.3.4 Groundwater quality Within the Rugby Limestone Member concentrations of calcium, iron, magnesium, manganese, nickel, potassium, sodium, ammoniacal nitrogen, sulphate, chloride and electrical conductivity consistently exceed drinking water standards over the area of monitoring, suggesting these exceedances represent natural conditions. Cadmium and chromium are periodically also observed above drinking water standards. Similarly, within the Langport Member concentrations of iron, lead, calcium, magnesium, potassium-magnesium, nickel, sodium, ammoniacal nitrogen, electrical conductivity and sulphate consistently exceed drinking water standards over the area of monitoring, suggesting these exceedances represent natural

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CEMEX UK Cement Ltd Southam Quarry ROMP Environmental Statement

conditions. Cadmium, chloride and chromium are periodically observed above drinking water standards.

7.2.3.5 Local groundwater abstractions There are no licensed groundwater abstractions within 2km of Southam Quarry[5]. The HRA produced by Golders in 2004[6] reported that there are 4 licensed groundwater abstractions within a 5km radius of the site; the closest of which is 3.5km to the west of the site and is taken from the Mercia Mudstone Group. None of these abstractions are taken from the Rugby Limestone Member or the Langport Member. There is a disused pumping station, Southam Waterworks, which is located approximately 1.1km to the south-west of the quarry. This site comprised two water wells drilled into the Langport Member in 1914 and 1939. Abstraction from the site ceased in 1972 and the abstraction licence revoked in 1981. The reasons for this were stated as water quality and yield problems, pollution risk as this was a shallow source and the age of the pumping station. Pumping from the existing Spier’s Farm development is required to dewater the quarry. Pumping is carried out using a 100mm diameter suction pump rated at 62 l/s (225m3/h) for a delivery head of 80m. The pump is run for up to 25 hours per week or an average of 3.6 hours per day. Therefore, the average pumping rate is 804 m3/d. It is likely that the actual discharge rate and daily volume will be lower due to an increase in static head as the development is deepened and due to frictional losses.

7.2.3.6 Quarry Water Management A Section 106 agreement (planning ref S965/04/CM001) for dewatering Spiers Farm quarry required a water management scheme to be developed for Southam quarry to mitigate any negative impacts upon groundwater levels and flows to adjacent water courses. This has been in operation since 2008 and is summarised below: • Dewatering occurs from the current Spier’s Farm sump to the old quarry sump. • Under normal rainfall conditions the water level in the settlement lagoon is maintained at a minimum level in order to maintain storage capacity should this be required for high rainfall conditions. • Discharge of treated sewage effluent and site drainage to two existing consented points A (Kaye’s Arm of the Grand Union Canal) and B (tributary of the River Itchen). • In the unlikely event that dewatering has a detrimental impact on water levels in Stockton Reservoir, surface water from dewatering the Spier’s Farm excavation should be pumped to the settlement lagoon for discharge to the reservoir (in accordance with Condition 6 of the planning permission and Paragraph 9 of the Section 106 agreement). Assuming that the water quality in the lagoon does not exceed Ecological Quality Standard (EQS) levels, water will be pumped from the settlement lagoon to the reservoir.

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CEMEX UK Cement Ltd Southam Quarry ROMP Environmental Statement

• During high rainfall conditions, if the water level in the old quarry sump reaches 78mAOD and continues to increase, water will be diverted to the settlement lagoon for temporary storage. • During high rainfall conditions, assuming that the water quality in the lagoon does not exceed EQS levels, water will be pumped from the settlement lagoon to discharge points A and/or B. • The EA approved scheme includes a monitoring programme for groundwater levels, water flows and water quality.

7.3 Potential Impacts Associated with Quarry Operation

7.3.1 Geological Resource In Griffins Farm area IV, limestone and clay will be excavated in a series of discreet mineral horizons, referred to as Units A, B, and C using mechanical excavators. The chemical composition of the respective units is critical in securing the required quality and blend of material for use in the Rugby Cement Works. It is anticipated that a transition period of up to 7 years is required to allow for units A and B mineral to be worked from Griffins Farm area IV and blended with unit C mineral from Spiers Farm Phase 3. From year 7 all quarry extraction will be transferred to area IV and extraction of Unit C mineral from Spiers Farm Phase 3 will no longer be required. Future quarrying at Griffins Farm will expose the geology to the south of the A426 and is considered to be minor beneficial as it will enhance the site’s status a Local Geological Site.

7.3.2 Hydrogeological resource Future quarrying operations at Griffins Farm (area IV) will require dewatering of groundwater within the Lias Clays. The effect of dewatering is considered to be negligible, due to the distance to local groundwater abstractions. In addition, natural groundwater levels will be allowed to recover on cessation of quarrying in Spiers Farm quarry. The maximum extent of extraction is shown on Figure 7.1.

7.3.3 Potential impact on Holy Well Holy Well is a Scheduled Ancient Monument comprising a 3m diameter 0.83m deep artesian well at a ground elevation of between 75-75m AOD located in Southam, approximately 1.5km from the quarry. The source of water to this well is thought to be the limestone aquifer, the Langport Member. The well had experienced declining water levels since 1991 which was thought to be due to the dewatering at the quarry to allow the quarrying of the Langport Member to provide a sub-base for the Southam bypass. Dewatering ceased in 2006 which allowed water levels and flows to recover. Future quarrying operations do not propose to quarry the Langport Member (White Lias) and therefore the impacts are considered to be negligible.

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CEMEX UK Cement Ltd Southam Quarry ROMP Environmental Statement

7.4 Potential Impacts Associated with Restoration Following completion of mineral extraction in area IV, a large proportion of Griffins Farm quarry will be restored to open water. The final water level of the restoration lake will be a function of groundwater levels, rainfall and runoff from adjacent areas. The potential long-term impacts of the lake restoration may result in a locally reduced water table due to equilibration with groundwater and open water evaporation. The presence of open water in the restoration may lead to an increased rate of evaporation compared with the base case of evapotranspiration from grassland and crops. However these potential impacts are considered to be negligible.

7.5 Mitigation and residual effects It is recommended that the water management scheme is updated to incorporate the proposed dewatering of Griffins Farm, during the transition from working Spiers Farm to Griffins Farm. Monitoring of lake levels during quarrying will continue to prevent expansion of drawdown and will protect potential receptors, including Holy Well.

7.6 Summary

Potential impact Significance Mitigation Significance of residual impact Quarrying Hydrogeological resource Negligible Incorporation of area IV into Negligible the Water management Plan. Continued monitoring of groundwater monitoring wells Holy Well Negligible Incorporation of area IV into Negligible the Water management Plan. Continued monitoring of groundwater monitoring wells Restoration Restoration to open water Negligible Incorporation of area IV into Negligible the Water management Plan. Continued monitoring of groundwater monitoring wells

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